Avalanche Forecast

Fair - Due to variable snowpack conditions

A significant storm is expected to bring around 10cm new snow tonight and around 20cm on Thursday. Freezing levels are expected to peak at around 1600m on Thursday afternoon, meaning that some rain or sleet may fall at lower elevations during the storm. Ridgetop winds are expected to blow up to 80 km/h from the SW. On Friday, unsettled air that moves in behind the frontal system will continue to bring flurries or light snow, with around 5cm expected or maybe 10 cm to the south of the region. Winds should ease to moderate southwesterly. Freezing level will lower to around 1000m. On Saturday another storm could affect the region (models are disagreeing), bringing further snow and strong winds.

On Tuesday, a size 4 natural avalance occurred just to the north of the region initiating from an alpine start zone at 2500 m on a NE aspect. Experts considered this to be at least a 40 year event, and the slide pulled out mature timber. While not technically in the region, this event illustrates the magnitude of the avalanche problem in the region. On Monday, many natural avalanches occurred on all elevations in the Selkirks. Most were in the alpine, but some were also reported from treeline and below treeline elevations. In many cases, the failure layer was the mid-February surface hoar layer. Typical size was size 2, but several size 3 avalanches and one size 3.5 avalanche was reported, that set off a number of sympathetic avalanches on nearby features. In the Monashees, less activity was noted, with wind slab pockets reactive to human triggers up to size 1.5.On Sunday a fatal avalanche incident south of Revelstoke occurred. The initial police report is here:http://revelstoke.rcmp.ca/ViewPage.action?siteNodeId=503&languageId=1&contentId=24477. We'll try to post more details as they become available. Other human-triggered avalanches were reported up to size 2 and natural avalanches were reported up to size 3 on a variety of aspects and elevations. Recent avalanche activity builds on what has been a very active period of avalanche activity since the beginning of March.

The last 4 days or so have seen storm snow amounts around 50-60 cm; winds have been strong, mostly from the south or southwest with occasional easterly or southeasterly. This new snow covers old pencil hard wind slabs which were created by last week's strong W/SW winds. Storm snow remains readily triggerable, but it's starting to take heavier triggers (such as a big cornice) to get lower layers, such as old wind slabs, or the more deeply buried surface hoar layers to move. That being said, these layers may still be sensitive to human triggering in areas where the snowpack goes from thick to thin, rock outcroppings being the classic example of this kind of structure. The big lurking danger remains the early February Surface Hoar that is now around 100 - 200cm deep. The snow above this weak layer has been under the influence of warmth and time which has settled the snow into a thick cohesive slab. Obviously, when a slab almost as tall as the average Canadian releases, the consequences are severe. Operators in the region have been diligently gathering data on this weak layer; in snowpack tests, the layer fails in a sudden planar fashion indicating that it has the potential to propagate across large distances. These tests mesh with the large avalanches that have been observed in the region recently. Conditions have been favorable for cornice growth recently, as a result many ridge lines are sporting large cornices.